(1) Field of the Invention:
This invention relates to an electrographic process which makes use of a photosensitive screen.
(2) Description of the Prior Art:
As an electrographic process, an electrofax system, a xerox system, PIP (Persistent Internal Polarization) system etc. have heretofore been well known. Both the electrofax system and the xerox system make use of so-called carlson's process for the purpose of producing a picture image. For this purpose, the electrofax system employs a chargeable member composed of an electrically conductive support coated with a photoconductive layer formed of zinc oxide, while the xerox system employs a chargeable member composed of an electrically conductive support coated with a photoconductive layer formed of non-crystalline selenium. In both the electrofax system and the xerox system, the surface of the photoconductive layer is uniformly charged by a flow of corona ions and then the charged surface is illuminated by a manuscript image light. In the imagewise exposed area of the charged surface, the electric charge is discharged to produce thereon an electrostatic charge image corresponding to a manuscript image. Subsequently, the electrostatic charge image is developed by charged color particles to render the electrostatic charge image visible. In the electrofax system, the visible image is fixed, as is, to provide an electrographic image. In the xerox system, the visible image is transferred to another support such as a record sheet etc. and then fixed to provide an electrographic image.
The PIP system, particularly its modified NP system makes use of a photosensitive body mainly composed of an electrically conductive support, a photoconductive film and an insulating film. The photosensitive body is uniformly charged at the first time and then is illuminated by a manuscript image light and at the same time charged again. Subsequently, the overall surface of the charged photosensitive body is exposed to light to produce, on the insulating film, an electrostatic charge image corresponding to a manuscript image. The electrostatic charge image is developed by charged color particles to render the electrostatic charge image visible which is then transferred to another support such as a record sheet etc. and then fixed to provide an electrographic image.
In all of the above described conventional electrographic processes, the electrostatic charge image is produced on the photoconductive layer or the insulating film uniformly superimposed one upon the other, so that the resolving power of the final copy becomes degraded.
An electrographic process comprising producing, on a photosensitive screen having a number of fine meshes, a first electrostatic latent image corresponding to a manuscript image and modulating a flow of corona ions by the first electrostatic latent image to produce on, a dielectric coated record layer, a second electrostatic latent image, has also been proposed. Such conventional electrographic process is capable of producing a picture image through the first electrostatic latent image produced on the photosensitive screen having a number of fine meshes and hence it is possible to obtain a final copy having an excellent resolving power. This conventional process, however, has the drawback that it is difficult to manufacture the photosensitive screen.